<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html{
            font-size: 20px;
        }
        .box{
            width: 4rem;
            height: 3rem;
            font-size: 0.75rem;
            background-color: coral;
        }
        @media (min-width:320px){
           .box{
               font-size: 0.1rem;
               width: 10rem;
               height: 10rem;
           }
        }
        @media (min-width:640px){
           .box{
               background-color: red;
               font-size: 0.1rem;
               width: 20rem;
               height: 20rem;
           }
        }
        @media screen and (min-width:320) and (min-width:640) {
            .box{
                width: 2rem;
            }
        }
    </style>
</head>
<body>
    <div class="box">
        安河桥
    </div>
</body>
</html>